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6 Oct 2008

Volume 93, Issue 14, Articles (14xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 93, 141901 (2008); http://dx.doi.org/10.1063/1.2990662 (3 pages)

J. H. Han, K. B. Kim, S. Yi, J. M. Park, S. W. Sohn, T. E. Kim, D. H. Kim, J. Das, and J. Eckert
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Ionic liquid as additive to increase sensitivity, resolution, and diffraction efficiency of photopolymerizable hologram material

Hechun Lin, Peter W. Oliveira, and Michael Veith

Appl. Phys. Lett. 93, 141101 (2008); http://dx.doi.org/10.1063/1.2995851 (3 pages) | Cited 5 times

Online Publication Date: 6 October 2008

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Ionic liquid was used as additive in photosensitive photopolymerizable materials. Ionic liquid as additive in photopolymerizable hologram material increases the sensitivity, the resolution, and the refractive index modulation of the material efficiently, which present strong diffusion after stopping the exposure due to the diffusion-controlled polymerization in ionic liquid. The diffraction efficiency was raised up to the theoretical maximum of 34% in the thin hologram.
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42.40.Eq Holographic optical elements; holographic gratings
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
82.35.-x Polymers: properties; reactions; polymerization
42.70.Jk Polymers and organics
42.70.Ln Holographic recording materials; optical storage media

Enhanced high-gain harmonic generation for x-ray free-electron laser

Qika Jia

Appl. Phys. Lett. 93, 141102 (2008); http://dx.doi.org/10.1063/1.2993179 (3 pages) | Cited 8 times

Online Publication Date: 7 October 2008

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The harmonic generation free-electron laser (HG-FEL) is capable of producing temporally and spatially coherent pulses in the vacuum ultraviolet and shorter wavelength regions. In this letter an easy-to-implement scheme that significantly enhances the performance of HG-FEL and extends its short-wavelength range is proposed. By adding a short phase-reversed modulator after the dispersive section, the electron energy spread is reduced and simultaneously the electron microbunching is enhanced. Three-dimensional simulations demonstrate the energy spread reduction and the bunching enhancement and show that more powerful higher harmonic radiation can be obtained.
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41.60.Cr Free-electron lasers
42.55.Vc X- and γ-ray lasers
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Intersubband linewidths in quantum cascade laser designs

A. Wittmann, Y. Bonetti, J. Faist, E. Gini, and M. Giovannini

Appl. Phys. Lett. 93, 141103 (2008); http://dx.doi.org/10.1063/1.2993212 (3 pages) | Cited 24 times

Online Publication Date: 7 October 2008

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We present a model to a priori calculate the temperature and field dependent intersubband linewidth of the optical transition in quantum cascade laser designs. Besides intra- and intersubband lifetime broadening, it comprises interface roughness scattering based on the approach of Tsujino et al. [Appl. Phys. Lett. 86, 062113 (2005) ]. We verified our model with experimental data of quantum cascade lasers having different linewidths. Excellent agreement with the experiment was found for the two-phonon resonance design. Linewidths are slightly overestimated in the bound-to-continuum design. Differential gain and threshold current density are in excellent agreement for the two-phonon resonance design. Although the slope efficiency is somewhat underestimated at low temperatures, there is still reasonable agreement with the experiment.
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42.60.By Design of specific laser systems
42.55.Px Semiconductor lasers; laser diodes

Beryllium acceptor binding energy in AlN

A. Sedhain, T. M. Al Tahtamouni, J. Li, J. Y. Lin, and H. X. Jiang

Appl. Phys. Lett. 93, 141104 (2008); http://dx.doi.org/10.1063/1.2996977 (3 pages) | Cited 1 time

Online Publication Date: 7 October 2008

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The acceptor binding energy of an alternative dopant, Be, in AlN epilayers has been probed by time-resolved photoluminescence (PL) spectroscopy. The binding energy of excitons bound to Be acceptors in AlN is determined to be about 33 meV, which implies that the Be acceptor binding energy in AlN is about 0.33 eV in accordance with Haynes’ rule. The measured PL decay lifetimes of the acceptor-bound exciton transitions in Be- and Mg-doped AlN (93 and 119 ps, respectively) also indicate that the binding energy of Be acceptor is smaller than that of the most common acceptor dopant in AlN, namely, Mg. The smaller activation energy of Be in AlN has the potential to partly address the critical p-type doping issue in AlN- and Al-rich AlGaN by increasing the room temperature free hole concentration by ∼ 103 compared to the case of Mg doping.
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71.55.Eq III-V semiconductors
71.35.-y Excitons and related phenomena
61.72.uj III-V and II-VI semiconductors
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors

Coherent trapping of x-ray photons in crystal cavities in the picosecond regime

S.-Y. Chen, H.-H. Wu, Y.-Y. Chang, Y.-R. Lee, W.-H. Sun, S.-L. Chang, Yu. P. Stetsko, M.-T. Tang, M. Yabashi, and T. Ishikawa

Appl. Phys. Lett. 93, 141105 (2008); http://dx.doi.org/10.1063/1.2996275 (3 pages) | Cited 1 time

Online Publication Date: 7 October 2008

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We report on the trapping of 14 keV photons in periods of 1.11–1.67 ps by the 12 4 0 backdiffraction in two- and multiplate silicon single-crystal cavities of a few hundred micrometer size. The formation of standing waves inside the cavities ensures better coherence for the x rays. We anticipate that the transmitted x rays through this type of cavities can be used as a quasicoherent x-ray source for probing the dynamic structures of solids, liquids, and biological substances.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
07.85.-m X- and γ-ray instruments

Highly efficient low-voltage cathodoluminescence of LaF3:Ln3+ (Ln = Eu3+,Ce3+,Tb3+) spherical particles

Zhen-Ling Wang, H. L. W. Chan, Hiu-Ling Li, and J. H. Hao

Appl. Phys. Lett. 93, 141106 (2008); http://dx.doi.org/10.1063/1.2998582 (3 pages) | Cited 40 times

Online Publication Date: 8 October 2008

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Spherical particles of rare-earth doped LaF3 are synthesized through refluxing in glycerol/water media. The low-voltage cathodoluminescence of LaF3:Eu due to 5D0→7F1 and 5D0→7F2 transitions was found to be sensitive to the site that Eu3+ ions occupied. The luminous efficiency of LaF3:Ce3+, Tb3+ with green emission is improved from 1.53 to 2.02 lm/W compared with LaF3:Tb3+, due to the energy transfer processes from Ce3+ to Tb3+ ions. Our results suggest that the obtained spherical particles of rare-earth doped LaF3 are promising as highly efficient low-voltage cathodoluminescent phosphors, which have received considerably less attention.
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78.60.Hk Cathodoluminescence, ionoluminescence

Fiber laser pumped high average power single-cycle terahertz pulse source

Matthias C. Hoffmann, Ka-Lo Yeh, Harold Y. Hwang, Thomas S. Sosnowski, Bradley S. Prall, János Hebling, and Keith A. Nelson

Appl. Phys. Lett. 93, 141107 (2008); http://dx.doi.org/10.1063/1.2998609 (3 pages) | Cited 13 times

Online Publication Date: 9 October 2008

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Near single-cycle terahertz pulse generation from lithium niobate crystal by optical rectification of pulses from an Yb:fiber laser/amplifier system was investigated. The pump laser supplied 250 fs duration pulses with 14 μJ energy at up to 1 MHz repetition rate. The terahertz pulse energy and average power exceeded 0.25 nJ and 0.25 mW, respectively. The average power was more than ten times higher than corresponding values achieved by using GaP as the nonlinear crystal under similar pumping conditions.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.By Design of specific laser systems
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Terahertz heterodyne receiver with quantum cascade laser and hot electron bolometer mixer in a pulse tube cooler

H. Richter, A. D. Semenov, S. G. Pavlov, L. Mahler, A. Tredicucci, H. E. Beere, D. A. Ritchie, K. S. Il’in, M. Siegel, and H.-W. Hübers

Appl. Phys. Lett. 93, 141108 (2008); http://dx.doi.org/10.1063/1.2988896 (3 pages) | Cited 21 times

Online Publication Date: 10 October 2008

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A liquid cryogen-free terahertz heterodyne receiver in a pulse tube cooler has been realized. The receiver operates at 2.5 THz. It is based on a quantum cascade laser (QCL) as local oscillator and a hot electron bolometric mixer. A detailed study of the QCL beam quality yielded a beam propagation factor of 1.1–1.2. The double sideband noise temperature of the system is 2000 K and when corrected for optical losses in the signal path it is ∼ 800 K.
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42.55.Px Semiconductor lasers; laser diodes
42.79.-e Optical elements, devices, and systems
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

Terahertz surface plasmon polaritons on a helically grooved wire

A. I. Fernández-Domínguez, C. R. Williams, F. J. García-Vidal, L. Martín-Moreno, S. R. Andrews, and S. A. Maier

Appl. Phys. Lett. 93, 141109 (2008); http://dx.doi.org/10.1063/1.2988897 (3 pages) | Cited 9 times

Online Publication Date: 10 October 2008

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The propagation of tightly confined terahertz surface plasmon polaritons on a helically grooved metal wire has been studied both experimentally and theoretically. The periodic structure of such metawires allows the formation of surface electromagnetic modes with different azimuthal symmetry at wavelengths longer than the pitch. There is good agreement between the experimentally determined band edge frequencies of these modes and numerical calculations for the structure investigated.
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71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.68.+m Optical properties of surfaces
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Quantum effects on the formation of negative hydrogen ion by polarization electron capture in partially ionized dense hydrogen plasmas

Young-Dae Jung and Daiji Kato

Appl. Phys. Lett. 93, 141501 (2008); http://dx.doi.org/10.1063/1.2998629 (3 pages) | Cited 1 time

Online Publication Date: 10 October 2008

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The quantum effects on the formation of the negative hydrogen ion (H−) by the polarization electron capture process are investigated in partially ionized dense hydrogen plasmas. It is shown that the quantum effect strongly suppresses the electron capture radius as well as the cross section for the formation of the negative hydrogen ion. In addition, it has been found that the electron capture position is receded from the center of the projectile in decreasing the quantum effect of the plasma.
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52.20.Fs Electron collisions
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
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Formation of a bimodal eutectic structure in Ti–Fe–Sn alloys with enhanced plasticity

J. H. Han, K. B. Kim, S. Yi, J. M. Park, S. W. Sohn, T. E. Kim, D. H. Kim, J. Das, and J. Eckert

Appl. Phys. Lett. 93, 141901 (2008); http://dx.doi.org/10.1063/1.2990662 (3 pages) | Cited 29 times

Online Publication Date: 6 October 2008

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Microstructural investigations on a series of (Ti70.5Fe29.5)100−xSnx alloys with x = 5, 7, and 9 reveal that Sn addition is effective in introducing both structural and spatial heterogeneities in ultrafine eutectic composites stemming from a large temperature difference between two eutectic temperatures upon solidification. The microstructural heterogeneities in these ultrafine eutectic composites strongly enhance the room temperature compressive plasticity up to ∼ 15.7%.
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81.30.Fb Solidification
81.40.Lm Deformation, plasticity, and creep
62.20.fq Plasticity and superplasticity

Local control of spin polarization in a semiconductor by microscale current loops

Y. S. Chen, S. Halm, E. Neshataeva, T. Kümmell, G. Bacher, M. Wiater, T. Wojtowicz, and G. Karczewski

Appl. Phys. Lett. 93, 141902 (2008); http://dx.doi.org/10.1063/1.2993230 (3 pages) | Cited 6 times

Online Publication Date: 7 October 2008

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We demonstrate a method to electrically manipulate the spin polarization in a semiconductor on a micrometer length scale and a submicrosecond time scale. A variable magnetic field induced by a microscale current loop magnetizes the Mn2+ ions in a CdMnTe/CdMgTe diluted magnetic semiconductor quantum well, and via sp-d exchange interaction polarizes photogenerated electron-hole pairs. A maximum spin polarization degree of ±8.5% is obtained at 4.2 K without external magnetic field. The induced carrier spin polarization and the thermal heating of Mn2+ spins are resolved spatially and temporally by microphotoluminescence measurements.
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75.50.Pp Magnetic semiconductors
75.75.-c Magnetic properties of nanostructures
75.30.Et Exchange and superexchange interactions
78.47.jd Time resolved luminescence

Determination of helicities in unidirectional assemblies of graphitic or graphiticlike tubular structures

H. Jiang, D. P. Brown, P. Nikolaev, A. G. Nasibulin, and E. I. Kauppinen

Appl. Phys. Lett. 93, 141903 (2008); http://dx.doi.org/10.1063/1.2993217 (3 pages) | Cited 4 times

Online Publication Date: 8 October 2008

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Here we propose a universal method for the determination of all helicities present in unidirectional assemblies of hexagon-based graphitic or graphiticlike tubular structures, e.g., multiwalled or bundled carbon nanotubes (CNTs) or boron-nitride nanotubes and their structural analogs. A critical dimension characteristic of a fundamental structural property, i.e., the atomic bond length, is discerned from electron diffraction patterns by which all helicities present in the assemblies are identified. Using this method, we determine the helicity population in a single-walled CNT sample produced by laser ablation technique.
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61.46.Fg Nanotubes
52.38.Mf Laser ablation
79.20.Ds Laser-beam impact phenomena
61.72.Dd Experimental determination of defects by diffraction and scattering

Stress-induced and thermoelastic properties of Ni–Fe–Al melt-spun ribbon

V. A. Chernenko, B. Rajini Kanth, P. K. Mukhopadhyay, S. N. Kaul, E. Villa, A. Gambardella, and S. Besseghini

Appl. Phys. Lett. 93, 141904 (2008); http://dx.doi.org/10.1063/1.2998406 (3 pages) | Cited 1 time

Online Publication Date: 9 October 2008

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Lattice parameters, elastic modulus, internal friction, superelasticity, and shape memory effect are studied in the vicinity of martensitic transformation (MT) exhibited by the Ni55Fe20Al25 melt-spun ribbon. In comparison to the melt-spun ribbons of other ferromagnetic shape memory alloys, Ni–Fe–Al ribbon has abnormally low elastic modulus, a record-breaking strength (>350 MPa), and large recoverable strain (up to 5%) due to both the superelastic and ordinary shape memory effects. The critical stress versus temperature phase diagram consists of two straight lines, indicating the formation of different stress-induced martensitic phases. The structural and thermodynamic results proved to be self-consistent.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.30.Bx Phase diagrams of metals, alloys, and oxides
81.30.Kf Martensitic transformations
62.20.fg Shape-memory effect; yield stress; superelasticity

Influence of reaction with XeF2 on surface adhesion of Al and Al2O3 surfaces

Tianfu Zhang, Jeong Y. Park, Wenyu Huang, and Gabor A. Somorjai

Appl. Phys. Lett. 93, 141905 (2008); http://dx.doi.org/10.1063/1.2992632 (3 pages) | Cited 5 times

Online Publication Date: 10 October 2008

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The change in surface adhesion after fluorination of Al and Al2O3 surfaces using XeF2 was investigated with atomic force microscopy. The chemical interaction between XeF2 and Al and Al2O3 surfaces was studied by in situ x-ray photoelectron spectroscopy. Fresh Al and Al2O3 surfaces were obtained by etching top silicon layers of Si/Al and Si/Al2O3 with XeF2. The surface adhesion and chemical composition were measured after the exposure to air or annealing (at 200 °C under vacuum). The correlation between the adhesion force increase and presence of AlF3 on the surface was revealed.
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81.65.Cf Surface cleaning, etching, patterning
81.40.Gh Other heat and thermomechanical treatments
68.35.Np Adhesion
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.37.Ps Atomic force microscopy (AFM)
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Early stages of collapsing pentacene crystal by Au

Kyuwook Ihm, Sukmin Chung, Tai-Hee Kang, and Sang-Wook Cheong

Appl. Phys. Lett. 93, 141906 (2008); http://dx.doi.org/10.1063/1.2998539 (3 pages) | Cited 4 times

Online Publication Date: 10 October 2008

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The characteristic feature of metal contacts with gold on organics is deterioration of the organic crystals during the contact formation. The unveiled key challenge is to probe dynamic details of the microscopic evolution of the organic crystal when the atomic Au is introduced. Here, we report how the collapse of the pentacene crystal is initiated even by a few Au atoms. Our results indicate that the gentle decoupling of intra and intermolecular π-π interactions causes the localization of the lowest unoccupied molecular orbital as well as the removal of cohesive forces between molecules, leading to the subsequent crystal collapse.
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68.35.Fx Diffusion; interface formation
68.43.Mn Adsorption kinetics
61.66.Hq Organic compounds

Experimental evidence of tetrahedral interstitial and bond-centered Er in Ge

S. Decoster, B. De Vries, U. Wahl, J. G. Correia, and A. Vantomme

Appl. Phys. Lett. 93, 141907 (2008); http://dx.doi.org/10.1063/1.2996280 (3 pages) | Cited 8 times

Online Publication Date: 10 October 2008

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We report on an emission channeling study of the lattice site location of implanted Er in Ge together with its thermal stability. We found direct experimental evidence of Er atoms located on the tetrahedral (T) interstitial site and on the bond-centered (BC) site, with a maximum total occupancy after annealing at 400 °C. Whereas Er is expected to occupy the T site in a diamond crystal structure, the observation of BC Er in Ge is more surprising and believed to be related to the Er-vacancy defect in the split-vacancy complex configuration.
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61.72.jj Interstitials
61.66.-f Structure of specific crystalline solids
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Observation of individual dopants in a thin silicon layer by low temperature Kelvin Probe Force Microscope

Maciej Ligowski, Daniel Moraru, Miftahul Anwar, Takeshi Mizuno, Ryszard Jablonski, and Michiharu Tabe

Appl. Phys. Lett. 93, 142101 (2008); http://dx.doi.org/10.1063/1.2992202 (3 pages) | Cited 19 times

Online Publication Date: 6 October 2008

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Detection of individual dopants in the thin silicon layer using Kelvin Probe Force Microscopy is presented. The analysis of the surface potential images taken at low temperatures (13 K) on n-type and p-type samples reveals local potential fluctuations that can be attributed to single phosphorus and boron atoms, respectively. Results are confirmed by simulation of surface potential induced by dopants and by the back gate voltage dependence of the measured potential.
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68.35.bg Semiconductors
68.37.Ps Atomic force microscopy (AFM)
61.72.S- Impurities in crystals

Gated armchair nanotube and metallic field effect

Wei Ren, T. H. Cho, T. C. Leung, and C. T. Chan

Appl. Phys. Lett. 93, 142102 (2008); http://dx.doi.org/10.1063/1.2998394 (3 pages) | Cited 6 times

Online Publication Date: 7 October 2008

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We propose a useful metallic field effect element based on the electric field control of armchair single-wall carbon nanotube. The electron conduction channels are enhanced by imposing a transverse gate voltage. Multiple Dirac points have been revealed theoretically by our density functional and tight binding calculations. Our electron transport results show that the performance of such unique transistors depends mainly on the diameter of nanotube exploited. The critical field strength required decreases rapidly with the tube diameter.
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85.30.Tv Field effect devices
85.35.Kt Nanotube devices

Phase separation and optical properties in oxygen-rich InN films

A. Dixit, C. Sudakar, R. Naik, G. Lawes, J. S. Thakur, E. F. McCullen, G. W. Auner, and V. M. Naik

Appl. Phys. Lett. 93, 142103 (2008); http://dx.doi.org/10.1063/1.2963498 (3 pages) | Cited 4 times

Online Publication Date: 7 October 2008

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We have investigated the properties of sputter deposited InN thin films prepared from an In-metal (InN-MT) and an In2O3 target (InN-OT). The excess oxygen present in the InN-OT films alters the microstructure by introducing additional disorder. Depth dependent x-ray photoelectron spectroscopy measurements indicate the presence of higher concentrations of oxygen in InN-OT. Raman spectra show evidence for the presence of an In2O3 secondary phase in both samples. Although the InN-OT film has a higher oxygen concentration, both films show similar electrical and optical properties.
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68.35.Dv Composition, segregation; defects and impurities
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.55.Nq Composition and phase identification
79.60.Ht Disordered structures
78.35.+c Brillouin and Rayleigh scattering; other light scattering

Magnetoelectric bistabilities in ferromagnetic resonant tunneling structures

Christian Ertler

Appl. Phys. Lett. 93, 142104 (2008); http://dx.doi.org/10.1063/1.2998697 (3 pages) | Cited 1 time

Online Publication Date: 7 October 2008

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The conditions for the occurrence of pronounced magnetoelectric bistabilities in the resonant tunneling through a ferromagnetic quantum well are theoretically investigated. The bistability appears due to the mutual feedback of the carriers Coulomb interaction and the carriers exchange coupling with magnetic impurities in the well. It is shown that the well Curie temperature depends strongly on the relative alignment of the quantum well level and the reservoirs chemical potentials, which can be modified electrically. Switching between a “current-on/magnetism-off” and a “current-off/magnetism-on” mode becomes possible if the well temperature lies in-between the bistable values of the well Curie temperature.
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75.80.+q Magnetomechanical effects, magnetostriction
73.63.Hs Quantum wells
73.40.Gk Tunneling
75.30.Et Exchange and superexchange interactions
75.30.Hx Magnetic impurity interactions
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Enhancing electron transport in Si:P delta-doped devices by rapid thermal anneal

K. E. J. Goh, Y. Augarten, L. Oberbeck, and M. Y. Simmons

Appl. Phys. Lett. 93, 142105 (2008); http://dx.doi.org/10.1063/1.2996582 (3 pages) | Cited 3 times

Online Publication Date: 8 October 2008

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We address the use of rapid thermal anneal (RTA) to enhance electron mobility and phase coherent transport in Si:P δ-doped devices encapsulated by low temperature Si molecular beam epitaxy while minimizing dopant diffusion. RTA temperatures of 500–700 °C were applied to δ-doped layers encapsulated at 250 °C. From 4.2 K magnetotransport measurements, we find that the improved crystal quality after RTA increases the mobility/mean free path by ∼ 40% and the phase coherence length by ∼ 25%. Our results suggest that the initial capping layer has near optimal crystal quality and transport improvement achieved by a RTA is limited.
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81.05.Cy Elemental semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.Cc Kinetics of defect formation and annealing
61.72.uf Ge and Si
72.20.Fr Low-field transport and mobility; piezoresistance
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.80.Cw Elemental semiconductors

Charging effect of Al2O3 thin films containing Al nanocrystals

Y. Liu, T. P. Chen, W. Zhu, M. Yang, Z. H. Cen, J. I. Wong, Y. B. Li, S. Zhang, X. B. Chen, and S. Fung

Appl. Phys. Lett. 93, 142106 (2008); http://dx.doi.org/10.1063/1.2994695 (3 pages) | Cited 5 times

Online Publication Date: 9 October 2008

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In this work, Al2O3 thin film containing Al nanocrystals (nc-Al) is deposited on Si substrate by radio frequency sputtering to form a metal-insulator-semiconductor structure. Both electron and hole trapping in nc-Al are observed. The charge storage ability of the nc-Al/Al2O3 thin films provides the possibility of memory applications. Charging in the nc-Al also leads to a change in the dc resistance of the thin films, namely, the electron trapping in the nc-Al leads to an increase in the resistance, whereas the resistance is reduced if there is hole trapping in the nc-Al.
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68.55.aj Insulators
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
81.15.Cd Deposition by sputtering
73.61.Ng Insulators
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Spin bias measurement based on a quantum point contact

Yanxia Xing, Qing-feng Sun, and Jian Wang

Appl. Phys. Lett. 93, 142107 (2008); http://dx.doi.org/10.1063/1.2999587 (3 pages) | Cited 12 times

Online Publication Date: 9 October 2008

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Electron charge transport through a quantum point contact (QPC) driven by an asymmetric spin bias (SB) is studied. A large charge current is induced when the transmission coefficient of the QPC jumps from one integer plateau to the next. Furthermore, for an open external circuit, the induced charge bias instead of the charge current is found to be quite large. It provides an efficient and practical way to detect SB by using a very simple device, a QPC or a STM tip. In addition, with the aid of magnetic field, polarization direction of the SB can also be determined.
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73.63.Rt Nanoscale contacts
72.25.-b Spin polarized transport
73.23.-b Electronic transport in mesoscopic systems

Low extended defect density nonpolar m-plane GaN by sidewall lateral epitaxial overgrowth

Kwang-Choong Kim, Mathew C. Schmidt, Feng Wu, Melvin B. McLaurin, Asako Hirai, Shuji Nakamura, Steven P. DenBaars, and James S. Speck

Appl. Phys. Lett. 93, 142108 (2008); http://dx.doi.org/10.1063/1.2908978 (3 pages) | Cited 4 times

Online Publication Date: 9 October 2008

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Sidewall lateral epitaxial overgrowth (SLEO) is demonstrated by metal organic chemical vapor deposition for nonpolar {1math00} m-plane GaN films. m-plane GaN films were grown by metal organic chemical vapor deposition on m-plane 6H SiC substrates with an AlN initiation layer. Subsequently, an SiO2 stripe dielectric pattern was formed with 2 μm window openings parallel to the [11math0] a-direction and an 8 μm mask and then the m-plane GaN was etched through the window openings to reveal Ga-face (0001) and N-face (000math) sidewalls. The SLEO growth was achieved in two growth steps—lateral growth from the sidewalls and subsequent growth through and then over the dielectric mask openings. In comparison to planar m-plane GaN films grown on 6H SiC, the threading dislocation density was reduced from low 1010 to 3×108 cm−2 and the stacking fault density was reduced by one order of magnitude.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.ag Semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Nn Stacking faults and other planar or extended defects
61.72.Lk Linear defects: dislocations, disclinations
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